RU2352878C1 - Gas-dynamic separation method - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: gas-dynamic separation method refers to the devices of low-temperature treatment of multi-component hydrocarbon gases (natural and oil ones), and is meant mainly for gas dehydration by condensing water component and (or) hydrocarbon components therefrom, and can be used in multi-component hydrocarbon gas collection, preparation and processing systems. Gas-dynamic separation method involves supply of high-pressure multi-component hydrocarbon gas flow to the nozzle, its isenthalpic expansion and cooling when passing through the nozzle, component condensation in cooled gas flow, condensate separation from gas phase, removal of cleaned gas and condensate, pressure increase of cleaned gas flow by its deceleration in diffuser. Original gas flow is pre-cooled by means of heat exchange with gas flow leaving the nozzle; components are condensed, separated from gas phase and removed at original gas pressure or (and) gas pressure after it has been expanded in the nozzle; gas phase is supplied to the nozzle after condensate is removed therefrom at original gas pressure, and pressure of expanded and cleaned gas flow is increased after its heat exchange with original gas.

EFFECT: improving gas-dynamic separation efficiency, and reducing energy consumption.

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Description

The invention relates to techniques for low-temperature processing of multicomponent hydrocarbon gases (natural and petroleum), namely for drying gas by condensation of water and (or) hydrocarbon components from it. The invention can be used in systems for the collection, preparation and processing of multicomponent hydrocarbon gases.

A known method of gas-dynamic separation [T. Bekirov, G. Lanchakov Gas and condensate processing technology. - M .: Nedra-Biznescentr LLC, 1999. - P.336], which includes the swirling flow of a high-pressure multicomponent hydrocarbon gas into the nozzle, its iso-enthalpy expansion with cooling upon expiration at a transonic speed, condensation of components from the expanded and cooled gas, deposition condensate from a rotating cooled gas stream onto a solid surface with the formation of a liquid film on it and removal of the latter through a slotted coaxial hole into the zone with reduced pressure, which is created by circulating ejection the formation of the gas phase from the source gas, increasing the pressure of the purified gas stream by braking it in the diffuser and supplying it to the consumer.

During isoenthalpic expansion of the gas in the nozzle when it expires at a transonic speed (300-360 m / s), the potential energy - gas pressure - passes into kinetic energy, while the gas cools and acquires a static temperature of about minus 50 ° С (at the initial gas temperature + 10 ° C). At low temperatures, condensation of the hydrocarbon components C _{3 + above} occurs. The stronger the cooling of the gas, the deeper its dehydration from the liquid (a decrease in the dew point of the condensed components). Therefore, to ensure the effective operation of the gas-dynamic separator, it is necessary to enhance the cooling of the gas, which is unattainable at transonic speeds.

Enhanced gas cooling is achieved in a gas-dynamic separation method [F.Akomoto, J.M. Braver, Ultrasonic gas preparation method // Oil and Gas Technologies, No. 6 - 2002 - P.41-44], including a swirling flow of a high-pressure multicomponent hydrocarbon gas into the nozzle, its isentalpic expansion with cooling upon expiration at a supersonic speed, condensation of components from the expanded and cooled gas, precipitation of condensate from a rotating cooled gas stream on a solid surface with the formation on it dkoy film and removing the latter through the slitted opening coaxial to the zone of reduced pressure which is created by circulation ejecting therefrom the gas phase source gas, raising the purified gas stream by means of its braking pressure in the diffuser and supplying it to the consumer.

When a gas flows at supersonic speeds, a static temperature in the flow of the order of minus 100 ° C is achieved and the condensation of the components from the gas is intensified.

However, at supersonic speeds, separating condensed components from a rotating cooled gas stream is inefficient. The high turbulence generated by the high velocities of gas outflow disrupts the settled liquid particles from a solid surface and carries them away from the gas-dynamic separator. Therefore, it is necessary to very quickly remove settled liquid particles from a solid surface in a zone with reduced pressure. The movement of settled particles is caused by the difference in pressure in the gas stream and in the zone of reduced pressure. In order to create a vacuum in this zone, gas is ejected from it by the source gas. Moreover, the larger the amount of gas ejected from this zone, the deeper the vacuum in this zone and the faster the settled liquid is removed from the solid surface. Together with the liquid, gas from the main stream enters the zone of reduced pressure. Therefore, a closed circulation movement of gas from the reduced pressure zone to the cooled stream and from the cooled stream back to this zone is obtained.

However, the creation of a zone with reduced pressure by circulating ejection of gas from it by the source gas leads to energy losses - pressure of the source gas. The loss of energy is greater, the deeper the created vacuum in the zone. But energy losses entail a decrease in the speed of the cooled gas and, as a consequence, an increase in its temperature and a decrease in the intensity of condensation of the components. Thus, the described technical contradiction leads to large energy expenditures in the form of gas pressure losses when implementing work on this method of a gas-dynamic separator.

A certain increase in the efficiency of gas-dynamic separation and a reduction in energy-gas pressure are achieved in the method (patent RU 2291736, priority 13.09.2004, IPC B01D 45/12, B01D 53/26), including supplying a swirling feed stream of high-pressure multicomponent hydrocarbon gas to the nozzle ; introducing into the initial stream of condensable components in the liquid or vapor phases; isoenthalpic expansion of the gas with cooling when it expires at a transonic or supersonic speed; condensation of components in an expanded and cooled rotating gas stream; separation from condensate gas; condensate collection in the zone with reduced pressure, which is created by ejecting from it a gas phase by a stream of purified gas; increasing the pressure of the purified gas stream by braking it in the diffuser; removal of purified gas and condensate; cooling the source gas with a liquid removed from the reduced pressure zone and / or purified gas.

However, in this method of gas-dynamic separation, the efficiency of trapping condensed components at supersonic speeds does not exceed 15 ÷ 20%. Energy losses in the form of pressure are also high and amount to about 30% of the initial pressure.

The objective of the present invention is to increase the efficiency of gas-dynamic separation and reduce energy costs - gas pressure.

The technical result in the implementation of the invention is achieved by the fact that in the gas-dynamic separation method, comprising supplying a stream of high-pressure multicomponent hydrocarbon gas to the nozzle, its iso-enthalpy expansion and cooling during flow in the nozzle, condensation of components in the cooled gas stream, separation of condensate from the gas phase, removal of purified gas and condensate, increasing the pressure of the purified gas stream by braking it in the diffuser, the initial gas stream is pre-cooled by heat exchange and with the flow of gas flowing from the nozzle, the components are condensed, separated from the gas phase and removed at the pressure of the source gas or (and) the pressure of the gas after its expansion in the nozzle, the gas phase is fed into the nozzle after it is cleaned of condensate at the pressure of the source gas, and the pressure of the expanded and purified gas stream is increased after its heat exchange with the source gas. Heat transfer is produced in countercurrent. During heat transfer, a helical motion is imparted to the source gas. In heat transfer, the feed gas is supplied through a capillary-porous structure. During heat transfer, hydrate formation inhibitors and / or absorbents are introduced into the feed gas.

Pre-cooling of the initial gas stream by heat exchange with the gas stream flowing from the nozzle, condensation of the components, separation from the gas phase and removal of the source gas and / or pressure after expansion of the gas in the nozzle under pressure, supply of the gas phase to the nozzle after it is cleaned of condensate at the pressure of the source gas, increasing the pressure of the expanded and purified gas stream after its heat exchange with the source gas made it possible to increase the efficiency of gas-dynamic separation and reduce energy costs - pressure g the basics.

The implementation of heat transfer in countercurrent, imparting a helical motion during the heat exchange to the source gas, supplying hydrate formation inhibitors and absorbents during heat exchange of the source gas through the capillary-porous structure, and also helps to achieve this goal during heat exchange.

The authors and applicants are not aware of gas-dynamic separation methods in which a technical result would be achieved in a similar manner.

Figure 1 - presents a diagram of the heat exchange of the source gas with cold expanded gas and diagrams depicting changes in pressure and temperature of the interacting flows during heat transfer.

Figure 2 - presents a diagram of the condensation of components from the source gas during heat transfer.

Figure 3 - presents a heat transfer scheme for the helical movement of the source gas.

In Fig.4 - shows a section aa in Fig.3.

5 is a diagram of a condensation process when supplying a source gas through a capillary-porous structure.

Figure 6 shows a heat transfer scheme with the supply of hydrate formation inhibitors and (or) absorbents to the source gas.

The method of gas-dynamic separation is as follows.

The cooling of the initial gas stream 1 (FIG. 1) by heat exchange with the gas stream 2 flowing out of the nozzle 3 allows sufficiently deep cooling of the gas at its initial high pressure P ₀ - diagram I (FIG. 1). The cooling of the source gas occurs from the maximum - the initial temperature T ₀ - plot II (figure 1), to a temperature T ₁ , the value of which can differ by 5 ÷ 10 degrees from the temperature T ₂ (plot III) of gas 2 at the exit of the nozzle 3.

Condensation of components 4 in the feed gas at a high feed pressure P ₀ and low temperature T ₁ increases the amount of liquid phase released from the gas, which ultimately improves the separation process.

The separation of the condensate 5 from the gas phase 6 at a pressure P _{0 of the} source gas and its low velocity, which is two orders of magnitude less than the speed of the gas 2 flowing out of the nozzle 3, allows you to effectively clean the gas phase from the liquid, for example due to gravity or filtration. This increases the efficiency of the separation process with virtually no pressure loss.

The removal of condensate 5 (Fig. 1) under the pressure of the source gas accelerates its removal from the area of condensation and separation from the gas, this also increases the separation efficiency.

The condensation of components 7 (Fig. 2) at a gas pressure after its expansion in the nozzle at the lowest possible temperature T ₂ - diagram III (Fig. 1) proceeds with maximum efficiency, especially at flow rates in the nozzle exceeding the speed of sound. With a decrease in the speed of such a gas-liquid flow, its pressure and temperature increase, and the condensate, evaporating, passes into the gas phase. Therefore, the separation of the condensate 7 (Fig.7) from the gas phase is most effective at gas pressure immediately after its expansion in the nozzle.

Removing this condensate 7 at an expanded gas pressure allows you to maintain a low temperature at which the condensate does not evaporate, which increases the efficiency of the separation process.

The condensation of components 4, 7 (FIG. 2), their separation from the gas phase and removal under pressure of the source gas and pressure after expansion of the gas in the nozzle 3 (FIG. 2) allows you to effectively clean the gas phase of the liquid condensed at high pressure, and from liquid 6, which was condensed at the lowest temperature T ₂ reached (plot III, FIG. 1), and thereby increase the efficiency of the separation process.

The supply of the gas phase 6 to the nozzle 3 (Fig. 1) after it is cleaned of condensate at the pressure of the source gas makes it possible to efficiently perform the process of iso-enthalpy expansion and cooling of the gas, without large expenditures of energy for condensation. This ultimately reduces the temperature T ₂ (plot III, figure 1) of the purified gas stream 2 and, as a result, the temperature T ₁ (plot II, figure 1) of the cooled feed gas, which in turn increases the number of condensable components 4 and separation efficiency in general.

The increase in pressure in the diffuser 8 (Fig.2) of the purified gas stream 2 after its heat exchange with the source gas 1 allows: firstly, to increase the temperature of the purified gas from T ₂ to T ₃ (plot III, figure 1), which can vary by 5 ÷ 10 degrees below the temperature T _{0 of the} source gas; secondly, increase the static flow pressure from the value of P ₂ (plot IV, FIG. 1) at the nozzle exit 3 to the value of P ₃ at the inlet of the diffuser 8 (FIG. 2), which is greater, the higher the temperature T ₃ . With this technique, the total energy of the purified gas stream 2 is increased, and when it is braked in the diffuser 8, the total pressure is restored to a value of P ₄ (plot IV, FIG. 1), which is only 15–20% lower than the pressure P _{0 of the} source gas. Thus, a reduction in energy costs - pressure.

Conducting heat transfer in countercurrent flow (FIGS. 1, 2) allows you to efficiently perform this process, increase the amount of condensate released from the gas, and thereby increase the efficiency of the separation process.

Giving during heat transfer to the source gas 1 (Figs. 3, 4) of a helical motion increases the time of its heat transfer, increases the efficiency of the latter, and ultimately increases the efficiency of the separation process.

The supply of the source gas during heat transfer through the capillary-porous structure 9 (Fig. 5) allows, due to capillary phenomena, to accelerate the condensation process and the separation efficiency.

The introduction of hydrate inhibitors into the source gas during its heat exchange allows preventing the occurrence of crystalline hydrates, which take up cold and at the same time, the condensation of the components deteriorates.

The introduction of absorbents into the source gas during its heat exchange allows expanding the capabilities of the gas-dynamic separation method and thereby increasing its efficiency. For example, input:

- kerosene fractions can increase the efficiency of condensation of hydrocarbon components in the temperature range 15 ÷ 40 ° C of the cooled gas 1 and prevent them from degassing when removing condensate, which ultimately increases the separation efficiency;

- diethylene glycol or triethylene glycol allows you to pre-drain the source gas from water vapor at temperatures of 15 ÷ 30 ° C, thereby reducing the energy costs of cold for its condensation, reduce the likelihood of crystalline hydrates and ultimately increase the efficiency of gas purification;

- monoethanolamine allows you to clean the gas from acidic components (CO ₂ and H ₂ S), thereby expanding the functionality of the method and ultimately increasing its effectiveness.

The implementation of the gas-dynamic separation method is illustrated by the following examples in the apparatus shown in figures 1-6. The multicomponent hydrocarbon gas feed is supplied to these devices. The composition of the source gas in mass fractions: CH ₄ - 0.778819; C ₂ H ₆ - 0.06861; C ₃ H ₈ - 0.041102; C ₄ H ₁₀ - 0.026154; C ₅ H ₁₂ - 0.01383; C _{6 + above} - 0.071485.

The source gas has thermodynamic parameters, which are presented in table 1.

Table 1 The initial parameters of the source gas No. Pp. Parameter Name Dimension Gas phase Liquid phase one 2 3 four 5 one Pressure, P ₀ MPa 16,0 16,0 2 Temperature, T ₀ ° C 40 40 3 Molecular mass 18.71 65.46 four Density kg / nm ³ 8,038 643.0 5 The proportion of phase, mass. 0,9951 0.0049 6 Viscosity Pass 1.91 10 ^-5 9.28 10 ^-2 7 C _p / c _v 1,816 8 Specific heat kJ / (kmol 62.22 145.90 9 Compressibility factor 0.7694

Example 1

The source multicomponent hydrocarbon gas 1 (FIGS. 1, 2) is supplied through an annular channel 10 between the cylindrical body 11 of the apparatus and the cylindrical thermo-gas-dynamic chamber 12. The source gas stream 1 is cooled by heat exchange in countercurrent with gas 2 flowing out of the nozzle 3. Gas at the outflow nozzle 3 has the initial parameters, which are presented in table 2. After cooling, stream 1 has the parameters shown in table 3. During cooling of the source gas 1, the hydrocarbon components 4 condense and separate from the gas phase due to gravity and in the filter 13 (Fig.1, 2) at a pressure of the initial flow. The liquid phase is discharged under the pressure of the source gas through the nozzle 14. The purified gas phase in front of the nozzle 3 has the parameters shown in table 4.

table 2 The initial parameters of the stream 2 at the exit of the nozzle 3 No. p. Parameter Name Dimension Gas phase Liquid phase one 2 3 four 5 one Expiration mode Mach number 1,5 2 Static pressure, P ₂ MPa 4,51 3 Static temperature, T ₂ ° C minus 88 four Mass fraction 0.9877 0.0123 5 Molecular weight of the phases 16,0 30.98 6 Phase density kg / m ³ 74.66 434 7 The specific heat of the phases kJ / (kmol deg.) 75.07 78.66 8 Compressibility factor 0.6041 9 C _p / c _v 1,125 10 Viscosity Pass 1,049 10 ^-5 1.28, 10 ^-4

Table 3 Parameters of flow 1 after heat exchange No. p. Parameter Name Dimension Gas phase Liquid phase one 2 3 four 5 one Pressure, P ₁ MPa 16,0 2 Temperature, T ₁ ° C minus 30 3 Mass fraction of phases in a supersonic flow 0.63 0.37 four Molecular weight of the phases 16,2 30.98 5 Phase density kg / m ³ 74.66 430 6 The specific heat of the phases kJ / (kmol deg.) 75.07 78.66 7 Compressibility factor 0.6041 9 C _p / c _v 1,125 10 Viscosity Pass 1,04910 ^-5 1.28 · 10 ^-4

Table 4 The parameters of the purified gas phase after the filter 13 in front of the nozzle 3 No. p. Parameter Name Dimension Gas phase Liquid phase one 2 3 four 5 one Pressure, P ₁ MPa 15.95 2 Temperature, T ₁ ° C Minus 30 3 Mass fraction of phases 0,999 0.001 four Molecular weight of the phases 16,2 30.98 5 Phase density kg / m ³ 74.66 434 6 The specific heat of the phases kJ / (kmol deg.) 75.07 78.66 7 Compressibility factor 0.6041 9 C _p / c _v 1,125 10 Viscosity Pass 1,04910 ^-5 1.28 · 10 ^-4

The purified gas phase is fed into the nozzle 3, in which it expands iso-enthalpy. The expanded flow at the exit of the nozzle 3 has the parameters shown in table 2. At a temperature of minus 88 ° C, additional condensation of hydrocarbon components occurs. The condensate is separated from the expanded and cooled gas 2 due to the vortex movement after the swirl 15. This condensate enters the chamber 16 and is discharged through the pipe 17 under the pressure of the expanded gas. After such cleaning, the gas phase has the parameters shown in table 5.

Table 5 Purified Stream Parameters 2 No. Pp. Parameter Name Dimension Gas phase Liquid phase one 2 3 four 5 one Expiration mode Mach number 1,5 2 Static pressure, P ₂ MPa 4,51 3 Static temperature, T ₂ ° C minus 88 four Mass fraction 0,9988 0.00012 5 Molecular weight of the phases 16.1 19.9 6 Phase density kg / m ³ 73.89 234 7 The specific heat of the phases kJ / (kmol gr.) 75.6 77.66 8 Compressibility factor 0.70 9 C _r / C _v 1,125 10 Viscosity Pass 1,04910 ^-5 1.28 · 10 ^-4

As the stream 2 of the gas phase thus purified is advancing through the thermodynamic chamber 11, it heats up during heat exchange with the source gas 1. In front of the diffuser 8, the heated stream of purified gas 2 has the parameters shown in Table 6.

In the diffuser 8, the cleaned gas stream is inhibited and restores pressure. The parameters of the cleaned stream after the diffuser are presented in table 7.

Table 6 Parameters of flow 2 at the inlet to the diffuser 8 No. p. Parameter Name Dimension Gas phase Liquid phase one 2 3 four 5 one Expiration mode Mach number 1,5 2 Static pressure, P ₃ MPa 4,5 3 Static temperature, T ₃ ° C minus 28 four Mass fraction 0,9999 0.0001 5 Molecular weight of the phases 16,2 20.98 6 Phase density Kg / m ³ 73.89 234 7 The specific heat of the phases kJ / (kmol deg.) 75.6 78.6 8 Compressibility factor 0.70 9 C _r / C _v 1,125 10 Viscosity Pass 1,04910 ^-5 1.28 · 10 ^-4

Table 7 Parameters of stream 2 at the outlet of the diffuser 8 No. p. Parameter Name Dimension Gas phase Liquid phase one 2 3 four 5 one Expiration mode Mach number M << 1 2 Speed m / s twenty 2 Static pressure, P ₄ MPa 13.34 3 Static temperature, T ₄ ° C plus 30.1 four Mass fraction 0,999999 0.000001 5 Molecular weight of the phases 16,2 19.87 6 Phase density kg / m ³ 90.66 237 7 The specific heat of the phases kJ / (kmol deg.) 75.62 78.67 8 Compressibility factor 0.75 9 C _r / C _v 1,125 10 Viscosity Pass 1,04910 ^-5 1.28 · 10 ^-4

The purified gas by the proposed method practically does not contain a liquid phase and has the following component composition: CH ₄ - 0.9969766; C ₂ H ₆ - 0.00301; C ₃ H ₈ 0.000012; C ₄ H ₁₀ 0.000011; C ₅ H ₁₂ - 0.0000003. It does not contain C _{6 +} components _above , and C ₃ H ₈ , C ₄ H ₁₀ , C ₅ H _{12 are} practically removed from it. Thus, the proposed gas-dynamic separation method is highly efficient. Moreover, the energy cost of its implementation is 16.25% of the initial pressure.

Example 2

When implementing the proposed method of gas-dynamic separation, giving during heat transfer to the source gas 1 a helical movement by twisting it through a tangentially installed inlet pipe 18 (Figs. 3, 4) increases its heat exchange time by 7 ÷ 10%. At the same time, the condensation efficiency of components increases by 1.5–3%. Due to centrifugal forces, it additionally increases the efficiency of separation of liquid from gas. In the complex, the efficiency of the separation process increases by 3 ÷ 4%.

Example 3

When implementing the method, the supply of the source gas through the capillary-porous structure 19 (Fig. 5), for example, through a cermet filtering material having capillary radii from 2 to 7 μm and a porosity of 0.3 ÷ 0.4, accelerates the condensation process. Due to capillary phenomena, the dew point temperature for all condensed components is reduced by 1.5 ÷ 2 ° C without the expense of pressure energy. The gas pressure energy costs are known to be estimated by the Joule-Thompson integral effect, which for hydrocarbons has a value of 0.33 ÷ 0.36 ° C per 0.1 MPa. Consequently, the reduction in pressure energy costs is 0.417 ÷ 0.606 MPa.

Example 4

When implementing the proposed method, the input (Fig. 6) into the feed gas during its heat exchange by a hydrate inhibitor, for example methanol, via pipeline 20 in several places 21-23 in the flow allows to prevent:

- the appearance of crystalline hydrates in the presence of water vapor in the gas, thereby reducing the cost of cold (respectively, pressure energy) for crystallization;

- emergencies associated with the shutdown of the hydrated sections by crystalline hydrates through which the treated gas flows.

This increases the energy efficiency and reliability of this separation method.

Example 5

The introduction of absorbents into the source gas during its heat exchange allows expanding the capabilities of the gas-dynamic separation method. For example, input:

- kerosene fractions through the pipeline 20 at three points of the apparatus 21-23 (Fig.6) allows to increase the condensation efficiency by 15-25% of hydrocarbon components in the temperature range of 15-40 ° C of the cooled gas 1 and to prevent their degassing when removing condensate, which increases separation efficiency;

- diethylene glycol or triethylene glycol allows you to pre-drain the source gas at temperatures of 15 ÷ 30 ° C from water vapor, thereby reducing the energy costs of cold for its condensation, reduce the likelihood of crystalline hydrates and ultimately increase the efficiency of gas purification;

- monoethanolamine allows you to clean the gas from acidic components (CO ₂ and H ₂ S), thereby expanding the functionality of the method and ultimately increasing its effectiveness.

Thus, in the claimed method of gas-dynamic separation, an increase in the efficiency of gas-dynamic separation and a reduction in energy costs - gas pressure were achieved.

Claims (5)

1. The method of gas-dynamic separation, including the flow of a high-pressure multicomponent hydrocarbon gas into the nozzle, its isoanthalic expansion and cooling during the flow in the nozzle, condensation of the components in the cooled gas stream, separation of the condensate from the gas phase, removal of the purified gas and condensate, increasing the pressure of the purified gas stream by braking it in the diffuser, characterized in that the initial gas stream is pre-cooled by heat exchange with the gas stream flowing from the nozzle, the components they are intensified, separated from the gas phase and removed at the pressure of the source gas or (and) the pressure of the gas after its expansion in the nozzle, the gas phase is fed to the nozzle after it is cleaned of condensate at the pressure of the source gas, and the pressure of the expanded and purified gas stream is increased after heat exchange with the source gas. 2. The method according to claim 1, characterized in that the heat exchange is produced in countercurrent. 3. The method according to claim 1, characterized in that during heat transfer to the source gas give a helical motion. 4. The method according to claim 1, characterized in that during heat transfer, the source gas is fed through a capillary-porous structure. 5. The method according to claim 1, characterized in that during heat transfer, hydrate formation inhibitors and (or) absorbents are introduced into the feed gas.

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